Electrics will not shut down

[Roger]

I wonder if anyone can point out what I have done wrong please? Did some work on the Mini dashboard but must have got some wires crossed when it went back. It is fitted with a "kill" switch which is in the main wire from the battery, but what I cannot understand is when I have the engine running and turn this off, nothing changes. I can take the ignition key out and the engine keeps running. How can power still be getting to the ignition, etc.??
Any help would be much appreciated

[rich@minispares.com]

The dynamo will be supplying power, so to kill the engine you need to put a break in the positive feed to the coil.

All you are doing by breaking the main power lead via the switch is preventing the battery from getting charged

[pad4]

Yup as Rich said - there are kill switches (FIA ones) and kill switches (Battery isolators) the FIA one has connections for the coil as well but the cheapo kill switch is nowt more than a isolator switch for the battery

Pad

[Roger]

Many thanks for the help. I think I understand a little more now. Will probably get some help to make sure it works properly, but you have told me what I need.

[steve65]

Surely turning it off at the ignition will kill it anyway? This will cut the power to the coil. The cut off switch is designed to kill the engine if you are unable to do this yourself, which is why the kill switch must cut off the coil etc.
The dynamo can supply power, but this should not be able to get to the coil with the ignition switch off.

[Roger]

Power is still getting there due to crossed wires. Following advice from here I know what the problem is and have arranged some help to sort it out.
Thanks

[rich@minispares.com]

Surely turning it off at the ignition will kill it anyway? .

not necessary as there are two sorts of 'kill switch' - and as they are normally there to be used when there is either panic (and the ignition cannot be found or reached), or tested by a scruiteneer, you cannot rely on been able to turn the ignition off by 'normal' methods

the 'immobiliser type' just cut the main battery cable when they are turned off, they are more of a theft deterrent - turning one of these of when the engine is running may not turn the engine off, particularly if the engine was revving, as the power made by the dynamo/alternator will allow coil to continue to operate.

the 'fia type' also have a switch built into to the bottom of the device, so that when the main battery is turned off, it also has the option of turning two (normally) other circuits off - its normal to wire the coil through this, so that the power is cut and the engine cannot run.

its obviously important to wire either type of switch correctly, with the ballest resistors that stop the alternators getting damaged if the key is turned off when the engine is running etc.

its also important to actually test and check that the wiring works - I recently saw a professionally built competition car that had the 'fia' cutoff part wired through the solenoid pulse wire - so it was as much use as a chocolate fireguard!

[dklawson]

As mentioned above the FIA switch is equipped with 3 pairs of contacts. One is for the main battery feed, one to interrupt coil power, and the third to dump the electricity in the loom to earth (through a dropping resistor).

The comments above focus on your car having a dynamo. If you have a later car with an alternator you need to focus on only using an FIA type switch with the dropping resistor. You do not want to disconnect the battery from the alternator with the engine running as it can damage the electronics in the alternator.

If you are turning off the ignition switch and the engine still refuses to stop there are a couple of other possibilities. The ignition switch can fail where it continues to supply power to the white wire(s) when the key is in the off position. Another possibility is failure of the electronics in the alternator. When that happens you typically see the red charge warning light on the dash remain on when the key is out of the ignition.

[steve65]

Turning off the ignition switch will kill the engine, how can the power get to the coil if its in the off position, you have broken the circuit? I understand what you are saying about the kill switch, but in this case he has turned the ignition key off too. Assuming the ignition switch is ok of course.

[dklawson]

Turning off the ignition switch will kill the engine, how can the power get to the coil if its in the off position, you have broken the circuit? I understand what you are saying about the kill switch, but in this case he has turned the ignition key off too. Assuming the ignition switch is ok of course.

If turning the key off stops the engine then the ignition switch is OK. If the complaint is that your car has a dynamo and turning the battery disconnect switch to the off position didn't kill then engine... I'm not sure that's a problem. Remember that the dynamo is producing electricity while the engine is running and it will be providing the power needed to run the ignition system.

If on the other hand you have an alternator that has failed diodes it is possible for it to back-feed power through the small brown/yellow wire all the way to the white wire on the ignition switch. That will keep the red charge warning light on when the key is out of the ignition. In some cases people have experienced enough back current flow to feed the coil (which is also powered off the white wire) and that can keep the engine running until you disconnect the wires from the coil.